-- | FIXME
module Codec.Audio.WavPack.Entropy
( EntropyData(..)
+
+ , clearMedian
+
+ , getMedian0
+ , getMedian1
+ , getMedian2
+
+ , incMedian0
+ , decMedian0
+ , incMedian1
+ , decMedian1
+ , incMedian2
+ , decMedian2
)
where
+import Data.Bits
import Data.Word
+import Prelude.Unicode
-- | FIXME
data EntropyData
= EntropyData {
-- | Median log2 values for a channel.
- edMedian ∷ !(Word32, Word32, Word32)
+ edMedian0 ∷ !Word32
+ , edMedian1 ∷ !Word32
+ , edMedian2 ∷ !Word32
-- | FIXME
, edSlowLevel ∷ !Word32
-- | FIXME
, edErrorLimit ∷ !Word32
}
deriving (Eq, Show)
+
+clearMedian ∷ EntropyData → EntropyData
+{-# INLINE clearMedian #-}
+clearMedian e = e {
+ edMedian0 = 0
+ , edMedian1 = 0
+ , edMedian2 = 0
+ }
+
+-- | The time constant of the 3 median level breakpoints
+div0, div1, div2 ∷ Word32
+div0 = 128 -- 5/ 7 of samples
+div1 = 64 -- 10/ 49 of samples
+div2 = 32 -- 20/343 of samples
+
+-- | Retrieve the specified median breakpoint (without frac; min = 1)
+getMedian0, getMedian1, getMedian2 ∷ EntropyData → Word32
+{-# INLINE getMedian0 #-}
+{-# INLINE getMedian1 #-}
+{-# INLINE getMedian2 #-}
+getMedian0 e = (edMedian0 e `shiftR` 4) + 1
+getMedian1 e = (edMedian1 e `shiftR` 4) + 1
+getMedian2 e = (edMedian2 e `shiftR` 4) + 1
+
+-- | Update the specified median breakpoints. Note that the median is
+-- incremented when the sample is higher than the median, else
+-- decremented. They are designed so that the median will never drop
+-- below 1 and the value is essentially stationary if there are 2
+-- increments for every 5 decrements.
+incMedian0, decMedian0, incMedian1, decMedian1, incMedian2, decMedian2 ∷ EntropyData → EntropyData
+incMedian0 e
+ = e { edMedian0 =
+ edMedian0 e + ((edMedian0 e + div0 ) `div` div0) ⋅ 5 }
+decMedian0 e
+ = e { edMedian0 =
+ edMedian0 e - ((edMedian0 e + (div0-2)) `div` div0) ⋅ 2 }
+incMedian1 e
+ = e { edMedian1 =
+ edMedian1 e + ((edMedian1 e + div1 ) `div` div1) ⋅ 5 }
+decMedian1 e
+ = e { edMedian1 =
+ edMedian1 e - ((edMedian1 e + (div1-2)) `div` div1) ⋅ 2 }
+incMedian2 e
+ = e { edMedian2 =
+ edMedian2 e + ((edMedian2 e + div2 ) `div` div2) ⋅ 5 }
+decMedian2 e
+ = e { edMedian2 =
+ edMedian2 e - ((edMedian2 e + (div2-2)) `div` div2) ⋅ 2 }